


The Adventure of the Buried River

by QMatchmaker888



Series: The (Mythology-Related) Adventures of Sherlock Holmes [2]
Category: Percy Jackson and the Olympians & Related Fandoms - All Media Types, Sherlock Holmes & Related Fandoms, Sherlock Holmes (1984 TV), Sherlock Holmes - Arthur Conan Doyle
Genre: ADHD Sherlock Holmes, Alternate Universe - Demigods, Alternate Universe - Mythology, Alternate Universe - Percy Jackson Fusion, Case Fic, Demigods, Gen, M/M, Marriage of Convenience, Mutual Pining, more tags to be added later
Language: English
Status: Completed
Published: 2021-01-05
Updated: 2021-03-02
Packaged: 2021-03-15 07:40:50
Rating: General Audiences
Warnings: No Archive Warnings Apply
Chapters: 7
Words: 10,086
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/28559961
Author URL: https://archiveofourown.org/users/QMatchmaker888/pseuds/QMatchmaker888
Summary: Sherlock Holmes (and crew) are on the verge of defeating Moriarty, but in order to capture him and his compatriots, they first have to trap them in their hideout, and to do that, they must venture into London’s labyrinthine sewer system. There they will face an unusually cheerful Roman goddess, an especially disgruntled river god, and creatures from other mythologies entirely.PLEASE NOTE: This is the second part of my ACD Sherlock Holmes Percy Jackson AU series. I’d highly recommend going back and reading part 1 first.
Relationships: Mary Morstan & John Watson, Sherlock Holmes & John Watson, Sherlock Holmes/John Watson
Series: The (Mythology-Related) Adventures of Sherlock Holmes [2]
Series URL: https://archiveofourown.org/series/1713991
Kudos: 5





	1. An Opening

**Author's Note:**

> Updates weekly, on Mondays or Tuesdays.

The sun was shining, flowers were blooming around patches of snow that had yet to melt, and Holmes and Watson were walking arm in arm through one of London’s public gardens. Despite the sun, a chill still hung in the air; Holmes could see his own breath clearly as he and the doctor wandered around, observing the new growth. Watson gently steered him towards a bed full of purple and yellow flowers. Daffodils and Hyacinths, Holmes recalled. He followed the son of Apollo without complaint. 

“Have you ever heard the story of how the Hyacinth was created?” the doctor asked him.

“I’m afraid not,” Holmes replied. He had read a great deal on the subject of Greek and Roman mythology since he had learned of its relevance to his life several months ago, but he hadn’t run into anything about Hyacinths.

“My father told it to me when I was younger,” Watson said, “Remind me to tell you later.”

“...When we’re not somewhere so public,” remained unsaid, but the detective received the message nonetheless. There were plenty of myths far too gruesome for the ears of the children playing nearby. He stifled a yawn. 

“Holmes…” Watson intoned worriedly. The detective had a bit of a habit of not getting as much sleep as he should when he was on a case.

“I had another strange dream last night,” he explained quickly.

His friend's face relaxed from one of worry to one of understanding. Strange dreams were common among demigods. 

“Was it your mother?” the doctor questioned.

Holmes paused for a moment before nodding. He had been dreaming of his godly mother, Athena, more and more since the Sphinx incident. In truth, it had been worrying him far more than he let on. Perhaps the odd dreams could be normal; Holmes was rather new to being a demigod, after all, but the way his friend spoke of Apollo, it seemed he had only met him a handful of times at most. The few other demigods he had met similarly only met their godly parents rarely, if at all. Yet he had dreamt of his mother over ten times in the course of the past few months. 

The two continued to walk in silence for a few more minutes, until bells began to toll in the distance. Then they spoke their goodbyes and parted ways, each missing the other’s warmth immediately upon leaving their side.

~*~*~*~*~*~*~

Later that evening there was a knock on the door of 221B Baker Street. 

“Come in, Lestrade!” Holmes called. He had seen the policeman walk up to the door through the window. As Lestrade opened the front door and made his way up the stairs, the detective ran through possible reasons for the visit. The most likely was a development in their investigation of the vast criminal network that had been revealed by the sphinx just the past winter. Working together with other demigods in London, Holmes and Lestrade had been able to track down and apprehend a large number of criminals connected to the network. Though the leaders and many of the most loyal members remained at large, they did have names for many of them, including the mastermind behind the operation, one James Moriarty. Unfortunately, they had run into a bit of a problem. They had amassed enough evidence against Moriarty and his compatriots, but they had to round most of the leadership up at once or else risk an organized counterattack.

“Mr. Holmes,” Inspector Lestrade said in greeting upon entering the flat, “I’m afraid we have a bit of a problem on our hands.” 

Holmes immediately noted the dirt caked on the man’s boots, a type found not by Scotland Yard, but by the jail in which the detective knew for a fact the most recently captured members of Moriarty’s network were being housed. Given that Lestrade had said “we,” combined with the fact that he had really only worked with the inspector on one thing recently, it was obvious that this had to do with one of them. He mentally ran through the list of criminals. Every one of them had already given them as much information as he suspected they would ever be willing to divulge. Taking into account Lestrade’s lack of observational skills and the fact that he clearly needed Holmes’ assistance in the matter, there was only one real possibility.

“Which one of them broke out?” he asked the inspector.

“That large scale robber, John Hagen,” Lestrade replied immediately, adding a second later, “I’m not going to ask how you figured that out.” 

Holmes paused for a moment. He wished he had his Watson here. He would certainly want to record this adventure, if only for his own personal records. Capturing Hagen had been quite an interesting escapade; the thief was a charmspeaker, relying on his silver tongue to manipulate people into giving what he wanted. He had been arrested several times before, but the charges were always dropped, partially due to his ability, partially due to the lawyers that had been hired for him by Moriarty. Holmes was fairly certain that tracking him down again would prove just as eventful a task as it had been the first time. 

“I thought you’d taken precautions against his charmspeak,” Holmes questioned, turning his attention back towards the Detective Inspector.

“We did. We made sure the keys to his cell were kept where his guards couldn’t access him,” Lestrade explained, hints of frustration and bewilderment creeping into his voice, “Unfortunately, it seems he had some additional tricks up his sleeve. He just got the guard out of the way and then somehow managed to escape the cell by himself, without picking the lock or damaging any part of the cell. We have no clue how he did it.”

“You’ve preserved the site for me to investigate then?” Holmes glanced at Lestrade, who nodded, “Good. Let’s get going.”

~*~*~*~*~*~*~

“There was no one else in this area but the guard. We thought it best to keep Hagen separate from the other prisoners,” Lestrade explained to Holmes as he unlocked the door to the cell in which, up until a few hours ago, John Hagen had resided.

A few other police officers and guards were present, but they stayed back, either looking on curiously or preoccupied with other matters. From the relative quiet, it was clear that this wing was mostly empty of prisoners, probably due to the recent construction of the place.

Holmes made a cursory inspection of the door, noting the lack of scratches around the lock, which indicated that it had not been picked. The door itself was undamaged, and a glance at the hinges showed him that they had not been removed anytime recently. The detective stepped into the cell; looking over the walls, ceiling, and floorboards, he found no signs of deliberate damage. Next he inspected the bed. No signs anything had been concealed in the mattress, no pieces loose or missing from the bed frame. Above the bed was a small window that came out of the building at ground level. 

Ah! he thought, getting up on the bed to inspect the opening more closely. The window was blocked by iron bars, and wasn’t big enough for a child to squeeze through, let alone a fully grown adult man, but that wouldn’t have stopped the sound of Hagen’s voice from making it to the ears of anyone who happened to be outside. Peering in between the bars, Holmes was pleased to note that the ground for at least a meter around the window in all directions was covered with nearly solid mud. Around the time of the escape, it would’ve been mostly congealed, but still wet; perfect conditions for clear footmarks.

The detective rushed outside, Inspector Lestrade trailing after him. The two men walked along the outside wall of the jail until Holmes spotted the cell window. 

“Ah ha!” he cried, crouching down to get a closer look. Immediately outside the window were bird tracks, probably those of a sparrow, leading only a half-foot from the window before they were replaced by a cat’s paw prints. The detective double checked; the window bars were certainly wide enough apart for a sparrow, or another bird of similar size to fit through. 

“Lestrade,” Holmes stated, “I believe we have a shapeshifter on our hands.”

The inspector blinked, shocked.

“A shapeshifter? But Hagen was a demigod,” he asked, clearly confused.

“I’m not surprised you haven’t heard of them,” Holmes replied, “The only modern examples of shapeshifting demigods are Roman.”

In fact, it was Watson who had told him about a particular line of demigods, descended from Neptune, who had the ability to shapeshift. Watson had told him a good deal about the world of demigods since the Sphynx incident several months ago, and he had also studied plenty on his own, first delving into Greek and Roman mythologies, then branching out into Egyptian and Norse, followed by a wide variety of European folklore. It never hurt to be prepared, and it gave him something to do between cases, which was more important than ever, as without Watson at his side, it became much easier for him to slip into one of his “dark moods,” as his friend referred to them. It was his own fault, really; he had grown too used to the doctor being a constant presence in his life. 

“Of course, there is also the possibility that our escapee’s… unique abilities have another mythology entirely to thank for their origin,” Holmes suggested after a moment’s thought. 

“Impossible!” Lestrade exclaimed, head snapping up.

“Is it?” the detective asked, “If the Greek and Roman mythologies hold some truth to them, why not others? A year ago you would have thought it impossible for distinct Roman versions of the Greek pantheon to exist, and yet here we are.”

“You can’t be serious,” Lestrade replied.

“Deadly. One must keep an eye on all possibilities, inspector.”

Holmes followed the tracks, first those of a sparrow found immediately outside the window, then those of a cat leading into the street, mostly obliterated by the traffic that had passed through since. Based on what little was still visible, he could discern that Hagen had been heading towards the middle of the street. Of course. There, in the middle of the street, was a manhole cover. The detective rushed over to inspect it. Like on the rest of the street, most traces had been destroyed, but he could still see a single cat footprint in the dirt on the metal disc. There were also other marks, ones that he had never once seen in the city. Remnants of a snake trail. 

The detective was certain now of his theory; John Hagen had escaped his cell as a bird, shifted into a cat (likely for his own safety; a cat was far more visible, and thus far less likely to be stepped on, than either a sparrow or a snake), before turning into a snake once he had reached the manhole so as to be able to flee into the sewers, where he had likely reverted to the form of a man. 

Hagen, being one of Moriarty’s most loyal confederates, would almost certainly have gone immediately to warn Moriarty of their investigation, which he undoubtedly knew of based upon how Lestrade had questioned him when he was first arrested. It could be a disaster for him, Lestrade, Mycroft… or anyone who was working with them to bring Moriarty down. 

This was why Holmes had been careful to leave Watson out of this case. He had deduced that Watson had put in a good deal of effort to protect him from the monsters that appeared before he knew of their existence. (Monsters must have appeared during that time; with two demigods living together, how could monsters not have taken notice?) He had only a vague idea to what lengths his Watson had gone to to protect him, but he intended to repay the favor. As much as it hurt him to leave his dearest friend out of his work, he would never forgive himself if harm came to Watson because of him. 

On a more practical note, Hagen’s hurry to warn his master had given them a valuable opportunity. The shapeshifter had fled into the sewers, so that was where Moriarty’s main base must be. That was where his closest lieutenants must reside. It was possible that the hideout wasn’t located in the sewers, but in that case the sewer must be a main entrance or exit, otherwise Hagen, a shapeshifter with a multitude of options for getting to Moriarty’s home base, would not have chosen to flee into the sewers. 

Holmes’ mind was already racing. They would have to act quickly to take advantage of this new information. The corners of his lips twitched upward into a ghost of a grin. He had a plan.


	2. The Team Assembles

**Notes for the Chapter:**

> Well I got this chapter done earlier than expected.

Mary Watson had always known she would die before she reached old age, she reflected as she poured tea into two teacups. After all, she was a child of Jupiter, and thus tended to attract monsters like the horse manure that filled the streets of London attracted flies. She passed one of the cups of tea to her guest, Ada Fisher, a daughter of Neptune and close friend of Mary’s.

“Have you heard anything from Mr. Holmes on the case?” Ada asked. She did not need to specify which case; there was only one that mattered enough to both of them for it to come up in conversation. The case of Professor Moriarty’s web and the prophecy surrounding it. For Ada, it was important because her brother had been killed, however indirectly, because of Moriarty. For Mary, it was important because she was fairly certain the prophecy foretold her death. 

“Not much. I think he and Lestrade have been a bit stuck,” Mary replied, “Most of what I hear comes secondhand through John.”

“John’s not working with Holmes on the case?” Ada said, surprised.

“No. Holmes tells him all about it, but refuses to let him in on the actual investigation. John’s not too happy about it, but I don’t think he’s going to force the matter. At least not yet, anyway,” Mary explained. 

“John’s in the prophecy, whether Holmes likes it or not,” Ada pointed out, sounding a bit exasperated.

Just then, there was a knock at the front door. Mary glanced out the window.

“Speak of the devil and he shall appear,” she said, a hint of amusement in her voice as she stood up to go greet Holmes. Ada raised her eyebrows. 

“Ah. Mrs. Watson,” the detective said in greeting, “Is your… husband home?”

“He’s in his study. Come in,” Mary replied, stepping aside so Holmes could enter. As he rushed past her, she noted the nervous energy in his manner, the way he never quite stood still. That could only mean one thing; there had been a new development in the case, the details of which the detective was eager to share with John. Mary headed back to the sitting room. She would hear about what had happened later, and with how much Holmes visited, she knew he knew his way to her husband’s study.

“He’s head over heels for John,” Ada commented, clearly just having realized what Mary had known since she had met the two of them.

(That had been quite an interesting day. Between the revelations about her mortal stepfather’s death and the multiple monster attacks that she and John had had to fight off together and scramble to keep a secret from Holmes, she had had quite a lot of things on her mind. The fact that she had noticed the detective’s… regard for his companion, her future husband, was either a tribute to her observational skills or evidence of how obvious Holmes’ feelings were, she wasn’t entirely sure which.)

“Indeed. I believe John reciprocates the feeling,” Mary confirmed, her exasperation at the pair’s inability to see what was right in front of them leaking into her voice.

“So are they…?” Ada asked in a conspiratorial tone, leaning in as though discussing a secret. 

“Unfortunately not. Their pining is becoming extremely tedious,” Mary replied. Ada already knew, from her friendship with Mary, that there was no romance between her and her husband; their marriage was simply a mutually beneficial agreement. Probably a good thing she knew, too, Mary reflected, otherwise she would have a lot more explaining to do.

“Oh gods, that reminds me of when me and John were at school,” Ada recalled, clearly holding back laughter, “You should’ve heard him. He would go on and on for hours about… I… I can’t remember the boy’s name.”

The mood dropped at that statement. They both knew about the forced separation of the Greek and Roman demigods and its aftereffects. It was not the sort of thing they discussed much. An awkward silence filled the air. Unsure of what to do, Mary laid a comforting hand on Ada’s arm.

Then the silence was broken by an indignant shout coming from upstairs.

~*~*~*~*~*~*~

“Holmes, how can you ask me to stay behind while you put yourself in such danger?” Watson shouted indignantly.

“I’m just going to block off the area around their hideout. I don’t expect to have to face any of Moriarty’s men,” the detective said coolly, “That part of the plan is up to Lestrade and his fellow Yarders.”

“You’ll be travelling through the sewers in an attempt to trap some of the most dangerous criminals in the country,” his friend argued, “What if something goes wrong? You’ll be far safer with me by your side, watching your back.”

“But you’d be far less safe. I cannot put you in danger for my sake,” Holmes stated, careful to keep his face an emotionless mask to hide the turmoil of emotions that seethed beneath it. He wanted Watson by his side. He had always wanted him by his side, which is why it had hurt so much when he left it to be  _ married _ . However, logically, he knew well how closely the public associated the two of them. If there was even the slightest hint of his friend’s involvement in this case, he would be assumed to be one of the main players. This wasn’t simply about what dangers would be found on this quest, though there would be plenty, but the dangers Watson would face if even a single member of Moriarty’s troupe managed to escape.

“Holmes, I am a demigod. I have been in danger my whole life,” the doctor stated, “and I will not let you take on this quest alone.”

The detective paused. He could hear the determination in Watson’s voice. There was no way he could get his friend to stay behind, short of knocking him unconscious and tying him to the heaviest piece of furniture he could find, and he preferred to avoid using that tactic whenever possible against criminals, let alone his closest (and only) friend.

“I should have known my Boswell couldn’t be swayed,” Holmes relented, a small smile making its way onto his lips even as dread filled his heart. 

“Thank you,” Watson replied in a tone of mingled relief and exasperation.

“We leave tomorrow at dawn, at Scotland Yard,” the detective said, businesslike, “The two of us will head down into the sewers, following John Hagen’s trail as best we can. We’ll block off any escape routes and then I’ll send an Iris message to Lestrade. The police will…”

“Just the two of you, going into the sewers by yourselves? I think not,” Mary’s voice interrupted from the doorway, “The sewers are connected to the Thames estuary.”

Both men quickly turned. Mary and Ms. Fisher were standing at the entrance of the study. They must’ve heard the two of them arguing from the floor below. Holmes opened his mouth to say something, but Ms. Fisher cut him off.

“The Thames estuary is a hotbed of aquatic monster activity, and it’s a known fact that it spills over into the sewers. You’ll need me and Mary down there. Besides, I have a stake in this too, or have you forgotten?”

Holmes already knew about the sewer’s dangers. He had done his research. There, all nearby monsters would immediately make a beeline for any demigod they could smell. Seeing as how he had already grudgingly agreed to let Watson join him, he supposed adding a few more people to their team wouldn’t hurt, and he knew the two women must be capable fighters; both were children of the so-called “big three,” and thus must have killed many monsters just to be standing here today. He supposed Ms. Fisher did have a point.

“Quests are usually supposed to have at least three people, aren’t they?” he said with a wry smile.

“Excellent,” Mary said matter of factly, “I’ll make sure to sharpen my throwing knives.”

Then she and Ms. Fisher turned down the hall to go back downstairs, chatting amiably about which weaponry to bring and what aquatic monsters they might encounter. Holmes mentally cursed his older brother, as he had done many times these past months, for not telling him that their mother was Athena until Sherlock had forced his hand. The detective had read as much as he could about the world of Greek myth in the months since the revelation that it was real, but he was still so far behind when it came to the one thing he could never quite make up for, firsthand experience.


	3. Into the Sewers

As the sun rose over London, Holmes took a cab to the pre-arranged meeting point near Fleet Street. He shivered; the morning air was cold, but he knew the sewers would be colder, more damp, and generally less pleasant. He was glad he had the foresight to wear his warmest attire. Lestrade, who was waiting at the intersection, nodded to him in greeting. Holmes began to pace back and forth, partially to warm up, partially to work off some of the restless energy building up within him.

A few minutes later, Watson arrived, his wife and Ms. Fisher just behind him. All three were wearing warm-looking, practical outfits. The doctor called out to Holmes in greeting, and he responded in kind, noting the bow and quiver of arrows slung over his friend’s shoulder, alongside a sturdy-looking bag, which, knowing him, almost definitely contained medical supplies. Mrs. Watson and Ms. Fisher were chatting quietly as they walked up. Mrs. Watson wore a sash of sorts in which ten gold throwing knives were sheathed. Ms. Fisher carried no visible armaments, but given the tendency for magical weapons to disguise themselves as everyday objects, that did not necessarily mean that she was unarmed. 

The five of them stood in a circle around a manhole in the middle of the street. Holmes could feel the warmth radiating from the doctor. He instinctively wanted to lean closer, but he willed himself to stay still. Watson’s steady presence at his side was a comfort, as always, despite his reservations about his friend coming along.

“Right then,” Lestrade spoke up, “We have several places we suspect as Moriarty’s hideouts marked. You four will be heading down into the sewers here, where Hagen was last seen. You’ll do your best to follow his trail. If that fails, Holmes’s memorized a map of the sewer system, so you can do a systematic search. It’ll take a good deal of time, but it’s better than nothing.”

Holmes’ mind wandered. He knew all of this already. Looking over the other four, Greeks and Romans working together, his mind went to John Hagen. They had thought, based on his charmspeaking, that he was a child of Aphrodite. He had used Greek terminology for the gods when questioned, like most of Moriarty’s men, so they had assumed that he was a Greek demigod, but the shapeshifting… Holmes had only ever heard of shapeshifting in Roman demigods, specifically a line of them descended from Poseidon. While their most famous ancestor had been Greek, they had been closely tied to Rome for centuries. Hagen himself had no ties to any other demigods, Greek or Roman, that they had been able to track down, aside from his fellows in Moriarty’s service. Holmes wondered if the thief had been like him, without a clue about his heritage and its associated gifts and dangers for most of his life. 

“...ladies first,” Lestrade finished, lifting the manhole cover.

Ms. Fisher nodded and descended into the sewer first, rearranging her sturdy-looking well-worn walking skirt. Mrs. Watson followed immediately behind, golden knives glinting sharply. When Holmes descended the rusty ladder after her, he was briefly surprised to find the sewers significantly drier than he had expected, and then realized that the foul liquid that would normally cover the bottom of the sewer was instead pressed up against the sides. Ms. Fisher stood proudly several meters down the tunnel, lantern in one hand, massive gold trident in the other, taking in the expression on Holmes’ face. Mrs. Watson stood next to her, checking all her knives were firmly in place. There was a dull thud behind the detective as his friend jumped down the last few rungs, then the manhole cover closed with a clang, and the only light was from the two lanterns they had brought down, one of which Holmes picked up, and Watson, who appeared to be glowing dimly. 

“Shall we?” the doctor asked with a tone of sarcastic joviality before setting off down the tunnel. The other three followed close behind.

~*~*~*~*~*~*~

Dr. Watson adjusted his quiver. Tension permeated the air almost as thickly as the stench of human waste. They had been walking through the tunnel for somewhere around five minutes, and no one had said a word. They were all too busy watching for the inevitable monster attack that had yet to come. 

“Aha!” Holmes cried, the sound echoing off the walls.

Watson jumped, and he was fairly sure Mary did the same. Holmes leant over an arrow-shaped chalk mark on the wall, nearly entirely obscured by the liquid Ada had redirected there to allow them to keep their feet dry. The daughter of Neptune must’ve seen it too, as the disgusting substance moved away from the mark, leaving it exposed.

“This is very recent,” the detective remarked. 

Watson could see his reasoning. The chalk was damp, though still clear and fresh upon the stone. With the damp that filled the sewers, there was no way a mark like that could last more than a week or two at most. The doctor recalled an earlier conversation with his friend in which Holmes had speculated that Moriarty’s men might use marks such as these to make their way around, seeing as it was unlikely that they’d all been able to get copies of a map. 

“I guess we’re going the right direction, then,” Mary commented.

Ada nodded, letting the water run back over the arrow, visibly relaxing as she did so. Watson realized the strength it must be taking her to hold the liquid up off the floor. If a fight broke out, she might have to let it fall back to the floor.

Mary quickly set off in the direction the arrow pointed, holding one of the lanterns. Ada followed only a few steps behind. The tunnel was small enough that they had to walk two by two, so that left Watson in the back, with Holmes at his side. The detective was carrying the other lantern in his left hand while his right held his gleaming bronze sword at the ready. 

“What a surprise!” a voice exclaimed from behind the party, “More demigods. Must be my lucky day!”

Watson whirled around, pulling an arrow from his quiver, knocking it on the string, and drawing back in one practiced motion. The others also readied their weapons. In the middle of the slime and human waste encrusted sewer stood a pale woman wearing a flowing robe the same color as the junk that hung on the walls. 

“People these days,” the woman scoffed, “no respect. And after all I’ve done for them.”

“Who are you?” Holmes spoke up. Watson’s grip tightened on the wood of his bow. 

“Who am I? Who am  _ I _ ?” the woman replied incredulously, “You barge into my domain, draw your weapons on me, and you don’t even know my name? After all I’ve done, after all the lives I’ve saved… people are so ungrateful these days.”

“You’re Cloacina,” Watson heard Mary state behind him, “Roman goddess of the sewers.”

“An utterly thankless job, I assure you,” Cloacina confirmed, smiling eerily.

Watson let up the tension on his bow string slightly, relaxing at the goddess’ words. Thankfully, she did not seem particularly intent on killing them, at least not at the moment, but if she did, there was little to nothing his arrows could do against a deity in their own domain. The doctor did not, however, put the arrow back in his quiver. Ada and Mary followed similar courses of action, lowering their weapons, but not their guard.

“ _ More _ demigods. So you’ve seen Moriarty’s men down here,” Holmes stated calmly, sword still held aloft in what Watson now realized greatly resembled a fencing en garde position, “Could you tell us where we can find them?”

The sewer goddess laughed, the noise echoing off the walls more loudly than seemed natural.

“You have some nerve,  _ Graecus _ ,” she said, tone suddenly menacing.

Watson froze, panic rising in his chest. 

“...You’re lucky I’m in a good mood,” Cloacina finished with a smile, “To answer your question; yes, I know where your quarry hides. I can show you, if you like.”

“What’s the catch?” Mary asked warily.

“The catch is that you’ll have to clear the way,” the sewer goddess’s smile did not waver, though there was now a bitterness built up behind it, “I, unfortunately, share my domain with many… less helpful beings.”

“So we go in front, clear away the monsters,” Holmes stated.

“Oh no, ordinary monsters steer clear of me. Why do you think you haven’t seen a single one since you came down here?” Cloacina asked, “The things we’ll have to get through are  _ much _ more powerful than that. They have as much control over their territories as I have over mine. And they don’t like me very much, so I’m afraid you’ll have to go ahead and… convince them to give us safe passage.”


	4. A Maze of Many Masters

“The things we’ll have to get through are  _ much _ more powerful than that. They have as much control over their territories as I have over mine. And they don’t like me very much, so I’m afraid you’ll have to go ahead and… convince them to give us safe passage.”

Mary’s hand clenched around one of her throwing knives. Typical. This woman was literally an  _ immortal  _ goddess, and she was still having them do the dangerous part. 

“I can’t actually do it myself, you know,” Cloacina said, as though reading Mary’s mind, “They’d never listen to me. So? What do you say?”

The group of demigods took their eyes off the sewer goddess, glancing among themselves. 

“Fine. We’ll do it,” Mary spoke up, forcing herself to relax, “So how many of your enemies are we dealing with?”

“Just one. The labyrinth isn’t my enemy, it simply resists my control. The Fleet on the other hand…” the sewer goddess replied.

“We’ll be going through the labyrinth?” Holmes interjected sharply, to Mary’s surprise. She knew he must have read up on mythology since discovering that it was all real, but the reality of the labyrinth was different enough from the stories that she’d assumed he wouldn’t have heard of it. John must’ve been talking to him about it more than she’d realized.

“Barely,” Cloacina replied, “Only the parts that overlap with my own domain. I know the way, but I don’t have as much control. We’ll need a key to get through any locked doors we may run into.”

“And where exactly is this key?” John asked in apparent frustration.

“It’s off that way,” the goddess gestured vaguely to the right of the way they had come, “In a maintenance area.”

“And ‘The Fleet’?” Holmes questioned.

“The river god in charge of the Fleet River. He doesn’t like me too much. Not happy he got buried underground and filled with human waste, I suppose,” Cloacina grinned smugly, “Just enter his territory, and he’ll come to you. It’s the sewer that runs under Fleet Street. You can’t miss it.”

Ada glanced at Mary, a mischievous look dancing in her eyes, and suddenly the daughter of Jupiter knew they were thinking the exact same thing. 

“Me and Mary will talk to the Fleet,” Ada spoke up, looking towards Holmes and John, “You two should go look for the key.”

John nodded, probably assuming that her reasoning was entirely practical, though Mary knew that that was only part of it. She knew the daughter of Neptune well; they had known each other since before she had met John, and so of course Mary knew of Ada’s tendency towards subtle matchmaking.

~*~*~*~*~*~*~

Holmes and Watson trudged through the foul liquid that ran along the floor of the sewer. Ada could only manipulate it precisely when she was nearby, so after the group had split up, the two men had had to contend with it properly for the first time since they had entered the tunnels. They paused at a four-way intersection. The doctor found himself immensely glad for his choice of footwear; if he had worn his regular shoes, he was certain his socks would’ve been soaked through by now. 

He glanced at the detective, looking down at the map, trying to find the quickest and safest route to the maintenance area where Cloacina had indicated the key would most likely be found (Which was easily spotted on the map due to the greenish-brown stain the goddess’ finger had left on the paper where she had touched it). Holmes’ eyes glittered in the glow of the lantern he carried. The dim light brought out the stark lines of his face; his sharp cheekbones, his aquiline nose…

Watson turned his attention back to the map. 

“I believe we ought to go this way,” Holmes declared, starting towards the middle tunnel. 

The doctor nodded and followed the son of Athena, who slowed slightly to match his companion’s pace. The two men walked in silence for a while. Then Holmes spoke.

“We have a long way to go yet. Some conversation would do us both good,” he stated, “You were going to tell me the myth behind that one flower?”

“The Hyacinth?” Watson asked. 

The detective only nodded in reply.

The son of Apollo felt a lump form in his throat. He had been meaning to tell Holmes the story at some point; it was one of his favorites, after all, if only for purely sentimental reasons, but something about the tunnels, the quiet echoing stillness, making it feel as though he and the detective were the only people in the world, made it feel far to intimate a setting for such a tale not to be imbued with a deeper meaning. He could only hope that his friend wouldn’t catch it.

“Remember Clio? Muse of history?” Watson began.

“How could I forget?” Holmes teased.

“Right. Well, back in Ancient Greece, she bore a son to the king of Sparta. That son was named Hyacinthus. He grew up to be quite handsome, according to my father,” the doctor paused, “Handsome enough for him to take him as a lover, anyway.”

Holmes looked up, shock visible in his eyes, but said nothing.

“Unfortunately for Hyacinthus, my father’s attentions weren’t the only ones he attracted. Zephyr, the god of the west wind, also fell in love with him,” Watson pushed on, “One day, Apollo and Hyacinthus were playing discus, or sometimes quoits—accounts vary, and my father himself never said anything either way—when Zepher, in a fit of jealous rage, shifted the winds, sending a discus or a quoits ring straight at Hyacinthus’ head, killing him. As he lay dying, my father turned him into a flower, the hyacinth.”

“I didn’t know Apollo was attracted to men,” the detective said sharply. Watson felt fear grip him. He pushed it away, attempting to make his face a mask of impartiality, though he was certain he was nowhere near and as good at it as Holmes.

“There are numerous myths about him falling in love with people of both sexes, male and female,” the doctor stated, putting as much effort as he could muster into keeping his voice steady and impassive.

“I suppose the tales of the former would have been swept under the rug by our modern-day historians,” Holmes commented sardonically.

“Exactly,” was all Watson could manage to say, the word mixed with a sigh of relief. Knowing the detective, he was probably mostly just critical of potentially useful knowledge being suppressed, but at least that seemed to be his greatest concern regarding the tale. 

They paused at another intersection.

“This way,” the son of Athena stated, guiding them down the tunnel to the left.

~*~*~*~*~*~*~

Holmes was fairly certain his hands were shaking. If they were, he desperately hoped Watson hadn’t noticed, or would at least, if he did, blame it on the chill that pervaded these foul-smelling tunnels. His gait disguised the effect it had on the lantern light well enough, he reassured himself. 

Had Holmes’ friend figured out his secret? Did he know the true strength of his regard for him? Perhaps he had only figured out part of it; maybe he had only deduced that he was an invert, and nothing more? Yet the two ideas were so closely linked in the detective’s mind; it seemed impossible that one could see one and not notice the other.

Or perhaps Watson knew nothing, and Holmes was simply over-analyzing. That was, as he had told his friend many times before, the problem with personal investment in an issue. At the very least, he now knew that the doctor did not seem to be disgusted by the idea of a man loving another man; he had volunteered to tell Holmes the story, after all, and there had been something in his voice, something sad, unsurprising considering the tragedy of the tale, but certainly nothing one would find in the voice of a man lecturing about immorality. 

There had been something else there too, something the detective couldn’t quite pin down. Some sort of tension, the nervousness that can only come from sharing something close to one’s heart. The obvious conclusion would be that Watson, to, was…

It took Holmes a good deal of effort to push the thought away. There was no use letting himself hope; the doctor was a married man, he scolded himself, and even if he wasn’t, why on earth would the son of Apollo ever fall in love with  _ him _ ?


	5. Mendelssohn’s Lieder

Holmes and Watson walked the rest of the way to the spot Cloacina had marked on the map in silence, each absorbed in their own anxieties. Thankfully, they didn’t run into any monsters along the way. The doctor had no clue if they were still close enough to the sewer goddess for the monsters to be kept at bay; they had walked quite a long distance since they had seen her, but then again, the only other explanation was sheer luck, and in Watson’s experience, that was something demigods tended to have very little of. 

“Watson! Here!” Holmes cried, rushing to a set of rungs embedded in the tunnel wall, forming a ladder not unlike the one they had used to enter this wretched place earlier that morning. 

Tied to one of the rungs with a piece of old, slimey twine was an ornate key. Though it looked to be older than the sewer itself, it still shone in the lantern light, highly incongruous to its surroundings. 

“You untie it, I’ll stand watch,” the son of Apollo replied.

The detective nodded and turned back towards his task. Watson glanced around, feeling uneasy. Then he heard a faint noise, echoing from further down the tunnel. A horse’s whinny. Glancing down, he could see that Holmes still hadn’t finished with the key. 

“Did you hear that?” the doctor hissed, readying his bow and arrow.

“What?” Holmes replied, looking up and noticing his friend’s distress at last.

“Sounded like a horse, probably actually a monster,” Watson explained in a whisper.

“I’ll hurry,” the detective said, nodding.

The sound came again, louder this time, more insistent. The doctor noticed Holmes stiffen next to him, and suddenly realized that this would only be the son of Athena’s second monster encounter, the first being the sphynx incident months ago, which hadn’t gone particularly well. The detective was an adult, living apart from other demigods, and it wasn’t like he was a child of one of the big three, so he had thankfully managed to avoid attracting attention thus far, even now that he knew the truth about what he was. Watson felt a pang of sympathy for his friend; he remembered the first few monsters he had faced well, even as the many others he had fought had blurred together in his mind. 

Holmes stood up slowly, as though trying not to make a sound. He held up the key to show that he’d managed to remove it successfully. The doctor nodded, and the two men began to back away, down the tunnel. If they were lucky, the monster hadn’t noticed them yet, and they would be able to escape. However, as Watson reminded himself grimly, demigods always had terrible luck.

Then the sound of a violin playing a familiar melody came, crisp and clear, from the same direction as the horse noises. It was a tune Watson had heard many times; a favorite, one he now associated with the man standing next to him. It was from Mendelssohn’s Lieder. The strangeness of hearing music like this in such a place was overwhelming, filling him with a sense of dread. 

Seconds after the song began, as though called by the music, there came a flood of water from behind Holmes and Watson, knocking them to the ground and shoving them forward, towards the mysterious violinist.

The doctor felt something hard strike his forehead, and then his vision went dark.

~*~*~*~*~*~*~

Luckily, just as the tide of foul sewer water crashed down onto him, Holmes managed to draw his sword. Not so luckily, the key slipped out of his hand. The detective cursed mentally, holding his breath to keep the liquid out of his mouth. He spread his limbs, using his hands and feet to steer himself away from the walls. The entire sewer had filled; the sluggish muck at the bottom of the tunnel had become fast-moving rapids. There weren’t more than a few inches of air at the top of the tunnel. 

Holmes couldn’t see a thing. He felt around for anything he could use. His right hand brushed up against something floating just ahead of him. It only took the detective a second to realize that it was Watson, who seemed to have gone limp, being pulled along by the current. It was only then that he felt the familiar sense of panic begin to rise up in his chest. It took more effort than he would’ve liked to shove the feeling down, which he blamed on the lack of oxygen. His thoughts was starting to feel fuzzy, but he forced himself to think.

The music was getting louder, and far from being muffled by the water, it seemed to be carried by it, as though the violinist were playing underwater. The rushing water pounding against the top of the tunnel sounded like hoof beats, except the sound was coming from below… 

Holmes reached down and felt the unmistakable stiff hair of a horse’s mane. He grabbed on. The horse bucked and tossed its head, and despite the detective’s best efforts, his hand began to slip. The music was right in his ear now, as loud as if he were playing it himself. The lack of air burned his lungs, but he stubbornly refused to breathe in. 

Then he felt something cold and metal brush against the hand still clinging to the horse’s mane. It was the key. He grabbed at it desperately; the twine was tangled in with the stiff hair, but thankfully, it came away easily, probably due to the sewer slime that coated everything.

The second Holmes got the key away from the horse, the water drained away, leaving only about a centimeter of eerily calm water along the bottom of the tunnel. The music stopped. The detective managed to land mostly on his feet, taking a few desperate breaths before he was clear-headed enough to assess the situation. Watson lay on his side, covered in sewer muck but thankfully still breathing; it was a terrible, rasping noise, but it meant the doctor was alive, so it sounded like music to Holmes’ ears. There was a trickle of foul water leaving Watson’s mouth.

The horse, whose white coat could barely be seen under the slime and rubbish that covered it, stood between Holmes and the doctor, looking at him with eyes that the detective could only think to describe as malicious. He readied his weapon, meeting the creature’s gaze, and forced himself to think. He knew he had heard something like this before. A white horse, sweeping people away in a rushing current, violin music… it certainly wasn’t from Greek myth, or Roman, for that matter. 

Holmes searched his memory for anything on the beast’s weaknesses. There were so many different stories, so many different versions, it might be difficult to know what would or wouldn’t work. Then, feeling the cold weight of the key in his left hand, the detective realized what had stopped the flood. Iron. The key was made out of iron, or possibly steel, which, according to some tales, would keep creatures like this at bay.

Watson began to stir, coughing water out of his lungs. Holmes ignored the swell of relief that filled him. Laying open, right by the doctor’s feet, was his medical bag. Surgical tools were often made of steel, the detective recalled. If he could just reach it…

The horse reared. Holmes backed up to avoid its hooves, and, on instinct, slashed at it. The blow should’ve killed the thing, but his sword passed through it with only a little resistance, like dragging a stick through a strong current. The horse only seemed annoyed at this, pawing the ground. Thinking quickly, the detective brandished the key in front of him, which seemed to slow the creature, but not stop it. 

Glancing over at Watson, Holmes saw him push himself into a sitting position, still coughing violently. There was a good deal of blood coming from a cut on the doctor’s forehead that he hadn’t been able to see from his previous angle. 

The horse reared again, and the detective backed out of the way, then cursed under his breath. The bag was now directly behind the horse; if he wanted to make a dash for it, he’d have to run between the creature’s legs. The only good thing Holmes could see was that it was no longer between him and Watson. The doctor was half sitting half leaning against the wall, probably still a bit dizzy from his head wound, but he seemed to be coughing less.

“Watson!” Holmes called, eyes not leaving the horse, “Would you be so kind as to pass me a scalpel?”

Out of the corner of his eye, he saw the doctor nod and slowly move towards the bag.

He swung at the monster again, a feint, to keep its attention away from Watson. It worked; the horse reared, this time managing to knock his sword out of his hand. It turned back to a handkerchief on the ground.

“Holmes!” Watson cried, voice hoarse, tossing a gleaming metal object at him. 

The detective caught the scalpel easily, plunging it into the horse’s neck. The creature let out a horrible, pained cry, then dissolved into a shower of water, slime, and trash. 


	6. London’s Lost Rivers

**Notes for the Chapter:**

> Ahhhh!!!! I forgot to post last Monday!

“Watson!” Holmes cried, the words piercing the doctor’s skull like a red-hot poker, “Are you all right?”

“I think I have a concussion,” the doctor groaned, closing his eyes, “I’ll be fine, I just need some ambrosia.”

There was a pause, and then the rustling noise of the detective digging around in Watson’s medical bag. 

“Here,” Holmes whispered urgently, placing a small square of ambrosia in the son of Apollo’s hand. 

The second Watson started eating he began to feel better. As the concussion faded and his head cleared, he attempted to process his blurry memories of the past few minutes. There had been a horse… and his friend had attacked it… and then he had asked Watson to throw him a scalpel? He got the feeling that the chain of events would only have made slightly more sense if he hadn’t been concussed when they were taking place.

“What in Hades’ name was that thing?,” Watson muttered, as he opened his eyes and gathered his strength to get up. 

“A Nokk, I think, also known as a Nack or Neck, or sometimes a Nixie,” Holmes replied, “They’re found in folklore from across Europe.”

“A nixie?” the doctor asked, incredulous, then, thinking for a moment, he sighed, “I suppose I shouldn’t be surprised.” 

“This, my dear Watson, is why it pays to study myths other than Greek and Roman,” his friend said, smiling shakily, “They’re traditionally river spirits; I assume this one lived here long before the sewers were built.”

Watson groaned and stood up, briefly scanning Holmes, who was now attempting to get as much of the filth as possible off of his handkerchief/sword, for injuries. Seeing no obvious injuries or signs that the detective was concealing any, aside from a few scrapes on the palms of his hands, which he carefully made note of, he turned his attention to gathering up his supplies. 

His quiver was still on his back, but the single arrow left inside had snapped in half. Arrows lay scattered about the tunnel. His bag was open, but most items were still inside or nearby. One of the two bottles of antiseptic had broken, spilling rubbing alcohol all over everything in the bag, which, all things considered, was not the worst that could’ve happened; all the tools would need to be cleaned and sterilized anyway. 

Watson was grateful that he had brought this bag instead of his usual one. This was a gift from his father, made to withstand the wear and tear of a typical demigod quest; his ordinary leather bag would have been destroyed by what’d just happened. Plus, it didn’t have a magical sterile pocket for bandages, so they would all have been rendered useless.

“Holmes, let me see your hands,” the son of Apollo instructed, getting out some bandages and the unbroken antiseptic bottle, “We don’t want you to get an infection.”

The detective obliged, and after that was taken care of, the two started to make their way back. Watson found a handful of arrows scattered through the tunnels and picked them up as they walked. They were useless as wet as they were, but hopefully Ada would be able to dry them off once they met up again.

~*~*~*~*~*~*~

Mary let out a grunt as she was thrown into the tunnel wall by the force of the water. Her and Ada’s attempt at diplomacy had failed miserably. Like most Potamoi, or Ancient Greek river gods, Fleet apparently had a temper, which had not been improved by being buried underground, incorporated into the sewer system, and filled with human waste. Go figure.

Fleet was also similar in appearance to most Potamoi; Huge and mostly human, with bull horns and assorted fish parts. Unlike other Potamoi, however, Fleet was a nasty shade of greenish-yellowish-brown, as opposed to blue or any other more typical river colors. 

Mary and Ada had, as Cloacina predicted, run into Fleet almost immediately after entering the sewer that used to be his river. They had asked, as respectfully as they could, if he would grant them passage. When that had failed, they had tried all the usual tricks, from flattery to bargaining to threats of retribution from Poseidon if the river god refused to cooperate. None worked. He did eventually agree, while charging full tilt at Ada, to let them pass if they could beat him in a fight. Since then, they had been fighting. The two demigods had gotten in a few good hits in the beginning, but Fleet had gotten more careful after realizing that the two women were better fighters than he had bargained for. 

Mary got up. Ada was trying to use the water to hold Fleet in place while she stabbed him with her trident, but he had power over the river too, and managed to break free. Mary turned her face upwards, looking through the small hole in the manhole cover at the blue sky above, half praying to her father, half trying to come up with a way to beat Fleet. She couldn’t summon lightning underground, and even if she could, water conducted electricity; she’d fry Ada along with the river god.

Wait. That was it. Water conducted electricity. So did iron, which she was fairly certain was what manhole covers were made from. A plan began to crystallize in the daughter of Jupiter’s mind. She waited for the right moment. 

Then Fleet charged at Mary. She sidestepped easily, and he charged past her. She threw one of her imperial gold knives after him; it whizzed past his head and imbedded itself in the stone.

“Hah!” the river god called, “You missed, foolish demigod.”

“No,” Mary replied, “I didn’t.”

She locked eyes with Ada, who was standing just a few feet in front of her, trident at the ready, then she glanced upward at the manhole cover. Ada’s eyes widened. She pushed the water away from her, up towards the manhole cover in one direction, over towards Fleet in the other, making sure there was still water on the walls connecting the two waves. Whatever the river god might’ve said in response to this was drowned out by a sudden crack as a bolt of lightning struck the manhole cover. Electricity spread through the water, and Mary used her powers to direct it towards her knife, and straight through Fleet, who promptly collapsed. It wouldn’t be enough to kill him, but hopefully he would be out for a while, and maybe next time he would think twice before messing with him.

“I wonder what the mortals thought of lightning striking a street in the middle of London,” Ada commented with a grin.

“Who knows?” Mary replied, returning the daughter of Neptune’s smile, “Let’s head back.”

The two women made their way through the sewer tunnels in relieved silence. By the time they returned the rendez-vous point, Cloacina had left, and their two demigod compatriots had yet to arrive. As they waited, a quiet excitement began to weave itself around them. They had both spent so long following the events that had led up to this from a distance, and now the conclusion was just around the corner. The feeling of anticipation was as strong in the air as the scent of human waste. It filled Mary with a sense of dread.

“Do you think this is where it ends?” Ada asked her, voice pained.

“No,” Mary replied truthfully, though a bit sadly, “I think this is where the end begins.”

“What do you mean?” Ada prodded, confusion evident.

“ _ To Reichenbach the three must fly _ ,” Mary quoted, “Reichenbach is the name of over a dozen different locations all across the continent. Whichever one the prophecy refers to, that’s where it will end. That’s where the final battle will take place.”

“I wish we knew which one it’ll be,” Ada commented.

“So do I,” Mary replied sardonically, then added, in a more serious tone, “Mr. Holmes, John, and I are the three it refers to. Don’t ask me how, but I’m sure of it.”

“Then…” Ada’s eyes widened, “ _ One love true and one to die _ . Oh, Mary…”

The daughter of Neptune leant over and embraced her so tightly she could hardly breathe.

“It’s okay,” Mary comforted, rubbing circles on her friends back as she wept, “I’ve come to terms with it.”

“No, it’s not okay,” Ada corrected, calming herself, “But things are so rarely okay for us demigods, are they?”

“I suppose there’s truth in that.”

The two women seperated. Ada opened her mouth to say something, but just then the sound of footsteps and voices came echoing through the tunnels. Holmes and John had returned. If the detective noticed their tear-stained faces, he didn’t make any comment.


	7. The End Begins

As soon as Holmes and Watson returned to the tunnel, where Mary and Ms. Fisher were waiting, Cloacina reappeared.

“Right,” she asked, “We’re all ready?”

Everyone nodded, too exhausted from their earlier ordeals to say much.

“Good,” the sewer goddess said, “Let’s go.”

She then turned around and began walking in the direction of the Fleet. The four demigods followed behind her as she made her way downriver. The atmosphere was tense. No one spoke, except for when Watson asked Ms. Fisher to dry off what arrows he had been able to salvage after being swept through the tunnels by the Nixie so he would be able to use them in the upcoming battle. She obliged.

After walking for a few minutes, the group’s path was blocked by an iron gate. Cloacina cleared her throat, making a disgusting gurgling noise, and held out her hand. Holmes gave her the hard-won key. She inserted it into the lock, and with a click, followed by the ungodly screech of hinges, the gate came open. The group continued for another minute or so before the sewer goddess halted.

“This is where I shall leave you,” she said, then, with a glint in her eye that worried Holmes slightly, she added, “many thanks.”

From there, it wasn’t particularly difficult to follow the echoing shouts and sounds of laughter to the hideout. The group paused, and using Ada’s powers and the light Watson emitted, plus a drachma Holmes had on hand, they sent an Iris message to Lestrade.

“You found them?” the detective inspector asked.

“Most likely suspected hideout B, though possibly C,” Holmes replied, nodding.

“Right,” Lestrade said, standing up, “time to move ou…”

His shout, clearly intended for others in the room with him, was cut off by him ending the call. 

~*~*~*~*~*~*~

From there, it had been fairly simple to block off all exits to the area of sewers surrounding Moriarty’s men’s hideout. Most of the work had been done for them; all but a few of the entrances had been blocked in an attempt to make the base easier to defend. It was simply a matter of standing guard at the two remaining tunnels and preventing anyone from escaping while Scotland Yard closed in from above. As it turned out, very few actually tried to escape through the sewers, most apparently opting to try to fight their way through the police.  _ Idiots _ , Holmes thought.

Once the chaos of the raid was over, the demigods were able to return to the surface and rest. Well, all of them but Holmes were able to rest, anyway. Lestrade had yet to ensure that every one of Moriarty’s men were captured, which was crucial. If any one of them had escaped, they could warn their leader, and they’d lose the element of surprise. 

Holmes paced around 221B Baker Street. Watson had insisted he head home to get some rest, but that would be impossible for him until he knew for sure. Lestrade had promised to alert him once he was done with the report.

There was a knock on the door. It was the detective inspector. By the time Holmes reached the door, Mrs. Hudson had already let him in.

“Mr. Holmes,” Lestrade said, his tone grave, “Colonel Moran has escaped.”

The detective took a breath to steady himself.

“Then it seems, inspector,” said Holmes, “that this game has only just begun.”


End file.
